Official 5e 2014 Dungeon Master's Guide Page 12
"Animism is the belief that spirits inhabit every part of the natural world. In an animistic worldview, everything has a spirit, from the grandest mountain to the lowliest rock, from the great ocean to a babbling brook, from the sun and moon to a fighter's ancestral sword. All these objects, and the spirits that inhabit them, are sentient, though some are more aware, alert, and intelligent than others. The most powerful spirits might even be considered deities. All are worthy of respect if not veneration.
Animists don't typically pay allegiance to one spirit over the others. Instead, they offer prayers and sacrifices to different spirits at different times, as appropriate to the situation. A pious character might make daily prayers and offerings to ancestor spirits and the spirits of the house, regular petitions to important spirits such as the Seven Fortunes of Good Luck, occasional sacrifices of incense to location spirits such as the spirit of a forest, and sporadic prayers to a host of other spirits as well.
An animistic religion is very tolerant. Most spirits don't care to whom a character also offers sacrifices, as long as they receive the sacrifices and respect they are due. As new religions spread through animist lands, those religions typically win adherents but not converts. People incorporate new spirits and deities into their prayers without displacing the old ones. Contemplatives and scholars adopt complex philosophical systems and practices without changing their belief in and respect for the spirits they already venerate.
Animism functions as a large tight pantheon. Animist clerics serve the pantheon as a whole, and so can choose any domain, representing a favorite spirit for that cleric."